1. Field of the Invention
The present invention relates to a redundant circuit of a semiconductor device and a method of producing the same, and more particularly relates to a redundant circuit of a semiconductor device including a fuse for laser trimming for replacing a circuit, and a method of producing the same.
2. Description of the Prior Art
A conventional redundant circuit of a semiconductor device utilizing a laser trimming, system is described in, for example, an article by Robert T. Smith et al., entitled "Laser Programmable Redundancy and Yield Improvement in a 64K DRAM," IEEE Journal of Solid-State Circuits, Vol. SC-16, No. 5, Oct. 1981.
FIG. 1A is a plan view showing an example of a conventional redundant circuit of a semiconductor device, FIG. 1B is a cross sectional view taken along a line B--B in FIG. 1A, and FIG. 1C is a cross sectional view taken along a line C--C in FIG. 1A.
Referring now to FIGS. 1A to 1C, a method of producing the conventional redundant circuit of a semiconductor device is described. First, a field oxide film 2 is formed on a silicon substrate 1, and a fuse 3b of polysilicon is formed on the field oxide film 2. Then, a PSG (Phospho Silicate Glass) film 4 is deposited on the field oxide film 2 and the fuse 3b by a CVD (Chemical Vapour Deposition) process. Subsequently, the PSG film 4 is selectively etched away utilizing a photoresist film (not shown), so that a part of the fuse 3b is exposed to form a contact hole 5. An aluminum interconnection 6 is then formed on the PSG film 4 and through and over the contact hole 5 so as to be connected to the fuse 3b, whereby the redundant circuit of a semiconductor device is completed.
FIG. 2 is a cross sectional view in which the fuse 3b of the redundant circuit shown in FIGS. 1A to 1C is disconnected. A circuit in a semiconductor device is ordinarily replaced by disconnecting a fuse included in a redundant circuit by irradiation of the laser beam. In FIG. 1C, laser beam energy irradiated on the PSG film 4 is absorbed in the fuse 3b. Consequently, the fuse 3b is fused and expanded, so that it is exploded and splashed with the PSG film 4 and disconnected as shown in FIG. 2. As a result of explosion and splash thereof, an opening 9 is formed in the PSG film 4 as shown in FIG. 2, the base width of which is identical to the line width 1.sub.1 of the fuse 3b.
When the redundant circuit as shown in FIGS. 1A to 1C is used, the line width 1.sub.1 of the fuse 3b must be kept large to some extent to reliably irradiate the laser beam. However, when the line width 1.sub.1 of the fuse 3b is large, the opening 9 formed after explosion thereof also becomes large, so that high integration of a semiconductor device becomes difficult. In addition, when the line width 1.sub.1 is large, the temperature difference under heat becomes large between the central portion and the end of the fuse 3bso that it becomes difficult to reliably disconnect the fuse 3b.